DESCRIPTION: Dr. Mayfield proposes to identify the components and molecular mechanism of translational activation of the chloroplast psbA mRNA. Genetic and biochemical analysis will be used in these studies which will be carried out in the green algae, Chlamydomonas reinhardtii. The general aims of Dr. Mayfield's laboratory are to study the interactions of the nuclear and organelle genomes in coordinate gene expression. The general objectives of this project are to identify the components and mechanisms which are used to regulate the translation of specific chloroplastic mRNAs in a light dependent manner. Dr. Mayfield's laboratory has isolated and characterized a set of proteins that bind specifically to the 5' untranslated region of the chloroplastic psbA mRNA. Genetic and biochemical analysis suggests that these proteins act in translational activation of the psbA mRNA. The molecular and genetic analysis of translational regulation in C. reinhardtii will help understand the basic principles in nuclear/organelle interaction in coordinate gene expression, and provide insight from a unique perspective into fundamental aspects of a translational regulation of gene expression. The specific goals are divided into two areas: the first is the genetic characterization of components required for psbA translation. Nuclear genes required for psbA translation will be isolated and characterized. And the RNA elements required for translational activation of psbA mRNA will be characterized. The second area is the biochemical characterization of psbA RNA binding and initiation complex formation. The proposed experiments include the characterization of the biochemical events that lead to activation of psbA RNA binding activity in response to light, and the characterization of the molecular mechanism of translational activation resulting from mRNA/protein interaction